Impact of Model Perfumes on Surfactant and Mixed Surfactant Self-Assembly

Abstract

The impact of some model perfumes on surfactant self-assembly has been investigated, using small-angle neutron scattering. A range of different model perfumes, with differing degrees of hydrophilicity/hydrophobicity, have been explored, and in order of increasing hydrophobicity include phenyl ethanol (PE), rose oxide (RO), limonene (LM), linalool (LL), and dihydrogen mercenol (DHM). The effect of their solubilization on the nonionic surfactant micelles of dodecaethylene monododecyl ether (C12EO12) and on the mixed surfactant aggregates of C12EO12 and the cationic dialkyl chain surfactant dihexadecyl dimethyl ammonium bromide (DHDAB) has been quantified. For PE and LL the effect of their solubilization on the micelle, mixed micelle/lamellar and lamellar regimes of the C12EO12/DHDAB mixtures, has also been determined. For the C12EO12 and mixed DHDAB/C12EO12 micelles PE is solubilized predominantly at the hydrophilic/hydrophobic interface, whereas the more hydrophobic perfumes, from RO to DHM, are solubilized predominantly in the hydrophobic core of the micelles. For the C12EO12 micelles, with increasing perfume concentration, the more hydrophobic perfumes (RO to DHM) promote micellar growth. Relatively modest growth is observed for RO and LM, whereas substantial growth is observed for LL and DHM. In contrast, for the addition of PE the C12EO12 micelles remain as relatively small globular micelles, with no significant growth. For the C12EO12/DHDAB mixed micelles, the pattern of behavior with the addition of perfume is broadly similar, except that the micellar growth with increasing perfume concentration for the more hydrophobic perfumes is less pronounced. In the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram, the addition of PE results in a less structured (less rigid) lamellar phase, and ultimately a shift toward a structure more consistent with a sponge or bicontinuous phase. In the mixed L1/Lbeta region of the phase diagram PE induces a slight shift in the coexistence from Lbeta toward L1. The addition of LL to the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram also results in a reduction in the lamellar structure (less rigid lamellae), and a shift toward a structure more consistent with a sponge or bicontinuous phase, or a coexisting phase of small vesicles. For the mixed L1/Lbeta region of the phase diagram LL induces a shift toward a greater L beta component.

Enhanced perfume surface delivery to interfaces using surfactant surface multilayer structures

“…The differences in location result in the surface multilayer structures existing over a wider range of surfactant/perfume compositions for phenylethanol than for linalool. This is in contrast to the trends observed in solution self-assembly [11], where linalool has a greater impact upon self-assembly than phenylethanol. …”

“…The only difference is that, consistent with previous arguments about the location of the more hydrophobic perfumes, such as LL, in self-assembled surfactant structures [11], it is assumed that the LL is located within the alkyl chain region (d 1 ) of the bilayer structure. Representative model fits for 80/20 mol ratio LAS-6/LL are shown in Fig.…”

“…4 for 70/30 mol ratio LAS-6/PE. It has previously been demonstrated at the interface [30] and in solution [9,11] that the more hydrophilic phenylethanol is preferentially located close to the headgroup region. Hence in the modeling of the data here it is assumed that the phenylethanol is in the region of the bilayer (d 2 ) occupied by the phenyl ring and headgroup.…”

“…A wide range of model perfume molecules with differing degrees of solubility and hydrophobicity have been studied, and include fragrance components such as phenyl ethanol, limonene, linalool, geraniol and eugenol. These studies have largely focused on aspects such as the solubilization in different surfactant systems [4][5][6][7][8], the location of the perfume molecule within the self-assembled structure [9], and their impact upon surfactant phase behavior [10][11][12]. In contrast there have been relatively few studies which have directly probed the co-adsorption of perfumes with surfactants at interfaces, or investigations in which the adsorption can be enhanced.…”

Behavior of cationic surfactants and short chain alcohols in mixed surface layers at water–air and polymer–water interfaces with regard to polymer wettability. I. Adsorption at water–air interface

“…Among a very large number of additives, alcohols hold a special place because they are the most common co-surfactants and co-solvents at their low and high concentration, respectively [1]. Addition of alcohols to surfactants influences the density and structure of mixed films at different interfaces and micelles in the bulk phase by changing their properties [1][2][3][4][5][6][7][8][9][10][11][12][13]. Even with abundant surface active agents and their mixtures in many products as well as in many industrial processes little is known how water molecules and those of surface active agents interact at water-air interface, particularly in mixed monolayer.…”